1. Field of the Invention
The present invention relates to a color image reading apparatus which is used in a color image transmitting apparatus, a color image copying apparatus, or the like.
2. Description of the Prior Art
A color image reading apparatus using a plurality of light sources having different spectrum characteristics has been proposed as a color image transmitting apparatus or a color image copying apparatus. As the light sources of a plurality of colors, for instance, there are used a red light source to selectively irradiate a red wavelength component, a green light source to selectively irradiate a green wavelength component, and a blue light source to selectively irradiate a blue wavelength component.
A fluorescent lamp has conventionally been used as a light source of each color to irradiate such wavelength components. Although the amount of light from the fluorescent lamp is large, in general, the flickering response speed is bad. Among the fluorescent lamps, the flickering response speed of the fluorescent lamp to emit the red light is particularly bad. Another drawback is that electric power consumption is large. Therefore, when the fluorescent lamp is used as a light source, there are limitations in realizing a high reading speed and to reduced the electric power consumption.
To solve such a problem, there has been proposed a color image reading apparatus in which a light emitting diode is used in place of a fluorescent lamp with respect to the light source having a slow flickering response speed. Thus, a fluorescent lamp and a light emitting diode are mixedly used as light sources of three colors, thereby making the reading speed high and reducing the electric power consumption (JP-A No. 60-130964).
FIG. 1 is a cross sectional view of a conventional color image reading apparatus in which a light emitting diode and a fluorescent lamp are mixedly used as light sources. In the color image reading apparatus, a reading section 2 is arranged near a glass plate 7 on which an original 1 onto which a color image is drawn by printing or the like is placed. A CCD line sensor 3 having a photo sensitive section 3a which faces the original 1 is attached to the reading section 2. The photo sensitive section 3a has a length corresponding to the width of the original 1. A multi-lens array 4 in which a plurality of rod-shaped lenses are arranged in a line is located between the photo sensitive section 3a of the CCD line sensor 3 and the original 1. The reflected light from one line, that is, a detected line l in the width direction of the original 1 is incident upon the photo sensitive section 3a of the CCD line sensor 3 through the multi-lens array 4.
A fluorescent lamp 5 having a length corresponding to the width of the original 1 is arranged near a side surface of the multi-lens array 4. A blue light is irradiated to the original 1 by the light emission of the fluorescent lamp 5. A light emitting diode unit 6 of the length W corresponding to the width of the original 1 is arranged near the side surface of the multi-lens array 4 on the side opposite to the fluorescent lamp 5. As shown in FIG. 3, according to the light emitting diode (hereinafter, simply referred to as the LED) unit 6, red LEDs 6R and green LEDs 6G are alternately arranged in a line on a base plate 6a. The LEDs 6R and 6G are covered by a rod lens 6b shown by an alternate long and short dash line.
Therefore, the red light and green light emitted from the red and green LEDs 6R and 6G are converged by the rod lens 6b and become the directional lights, thereby concentratedly irradiating the reading position of the original 1. On the other hand, the blue light from the fluorescent lamp 5 is irradiated to a wide range of the original 1 since it is the dispersive light.
When the original 1 is read, the respective color lights are time-sharingly irradiated. Every time each color light is irradiated, the reflected light from the original 1 is detected by the photo sensitive section 3a of the CCD line sensor 3 and is photoelectrically converted into an electric signal. The electric signals of the respective colors are simultaneously supplied to a color processing circuit through delay circuits. Three primary color signals of red, green, and blue corresponding to the mixture ratios of the respective color signals are formed, thereby obtaining color image signals.
When the LED unit 6 as a directional light source and the fluorescent lamp 5 as a non-directional light source are mixedly provided, there is a drawback such that if the original 1 floats over the glass plate 7, a color tone deviation occurs.
That is, for instance, when the original 1 has a crease or the like, the original 1 floats over the glass plate 7 as shown in a cross sectional view of FIG. 2. Since the LED unit 6 is the directional light source as mentioned above, the red and green lights from the LED unit 6 are concentratedly irradiated from the oblique lower position to the detected line % in a state in which the original 1 is in contact with the glass plate 7. Therefore, when the position of the detected line l is moved upward due to the floating of the original 1, the red and green lights are not sufficiently irradiated to the detected line Z. Thus, the reflected lights of the red and green lights which enter the CCD line sensor 3 remarkably decrease.
On the other hand, since the fluorescent lamp 5 is the non-directional light source, the blue light from the fluorescent lamp 5 is sufficiently irradiated to the detected line l even when the original 1 is floating. Therefore, the blue light which is reflected by the detected line l and enters the CCD line sensor 3 is not so largely reduced even if the original floats. Consequently, when the directional light source and the non-directional light source are mixedly provided, if the original 1 floats, the ratio of the reflected light of the light emitted from the non-directional light source is relatively high, so that there is a drawback such that the color tone deviation occurs and the color reproduction which is accurate to the original cannot be realized.